The present invention relates to an analog electronic timepiece with chronographic function, and in particular relates to a chronographic lap calculating circuit and hand driving control circuit for measuring a lap time during chronographic measurement.
In the past, conventional analog multifunction electronic timepieces display the elapsed time designated a split time hereinafter, however none display the time between two points of measurement designated a lap time hereinafter while the time is measured.
Explanation will be given about a split time and a lap time in detail. FIG. 2 is an explanatory diagram for explaining the function of the split and the lap measurements. Suppose that switching operation is performed three times after chronographic measurement starts in FIG. 2.
When a first switching operation occurs both a split time and a lap time indicate the time between the start and the first switching operation.
When a second switching operation occurs, a split time indicates the total time from start to the second switching operation, SPLIT2. On the other hand, lap time indicates the time between the first switching operation and the second switching operation, LAP2.
Furthermore, a split time and a lap time at each of three switching operation are shown in FIG. 2.
Namely, a split time indicates the total time from the start of the chronographic operation to the ultimate switching operation, and the lap time indicates the time between the two switching operations which are adjacent to each other.
Thus, when the switching operations are performed n times, the relationship between split time and lap time is governed by the following formula (1) is always valid. SPLIT(n)=LAP1+LAP2+. . .+LAP(n) . . . the formula(1)
The chronographic measurement is usually performed by the following operation.
An outer operating member starts to activate the timepiece, then an interrupting, or interrupt signal generating means for the chronograph is activated so as to generate interrupting, or interrupt signals at equal intervals of an arbitrary time.
There are usually two kind of interrupting signals and their time intervals are 1/10 second and 1 second, or 1/100 second and 1/10 second.
The chronograph measurement is performed by counting these interrupting signals with a counter and so on.
Particularly, in case of an electronic timepiece having an analog display, a hand driving control operation is periodically performed in order to move a hand to a position in a dial corresponding to the value indicated by the counter per 1/10 second or one second intervals depending upon the technical capability of the timepiece.
The value less than the unit of the interrupting signal is separately read in a chronograph hard counter etc. so as to display directly, or this function is not provided according to the technical specification of the product.
However, when a lap time is measured by accumulating interrupting signals, it is sometimes incorrectly measured as a value greater than its true value on account of the timing of the switching input. This is due to the fact that interrupt signals are generated in accordance with the passage of actual time and the issuance of interrupting signals is not synchronized with the commencement of a lap measurement.
This problem is illustrated by FIG. 3 which shows driving quantity of two cases of which the timing of switching input in response to an interrupting timing differ with each other.
In cases that are two complete interrupt cycles between an initial switching input and a final switching input. Thus, in both cases the time piece should display a lap time comprising two interruptions (two drive parts). Indeed this is true for case 1, wherein the two interrupt cycles occur between switching inputs A and C.
As for the case 2, however, switching input B is inputted just before the interruption 1 and as a result the drive 1 corresponding to the interruption 1 is performed at once. Consequently, rather than being performed for two interrupt periods, drive is performed for three interruptions in total until the next switching input C occurs. Therefore there exists a problem that the measured lap time data differs from the displaying lap time data.
It is possible to display a measured data correctly by setting back the hand which drives too much with a lap time calculation when the switching input C is inputted. However, such an operation requires a hand reversion driving circuit and at the same time, it is hard for a user to trust the displayed measurement of an electronic timepiece moving as described above.
If the chronograph interruption generating means and chronograph measuring means are restarted every switching input, it can be prevented that the hand drives too much. However, a problem occurs at the same time that the total time from the start is difficult to display when a measurement is finished.